Service area analysis
What is a service area?
With ArcGIS Network Analyst, you can find service areas around any location on a network. A network service area is a region that encompasses all accessible streets (that is, streets that are within a specified impedance). For instance, the 5-minute service area for a point on a network includes all the streets that can be reached within five minutes from that point.
Service areas created by Network Analyst also help evaluate accessibility. Concentric service areas show how accessibility varies with impedance. Once service areas are created, you can use them to identify how many people, how much land, or quantities of anything else within the neighborhood or region.
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Finding the network-based service area follows the same workflow as other network analyses.
Service area analysis layer
The service area analysis layer stores all the inputs, parameters, and results of a service area analysis.
Creating a service area analysis layer
You can create a service area analysis layer from the Network Analyst toolbar by clicking Network Analyst > New Service Area.
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When you create the service area analysis layer, it shows up in the Network Analyst window, along with its six network analysis classes—Facilities, Lines, Polygons, Point Barriers, Line Barriers, and Polygon Barriers.
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The service area analysis layer also appears in the table of contents as a composite layer that is named Service Area or, if a service area with the same name already exists in the map, Service Area 1, Service Area 2, and so on. There are six feature layers, which have default symbology that can be modified in their respective Layer Properties dialog boxes.
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Service area analysis classes
An overview of each class and descriptions of their properties are provided in the following sections.
Learn more about network analysis classes
Facilities class
This network analysis class stores the network locations that are used as facilities in service area analysis. The Facilities feature layer has three default symbols: Located, Unlocated, and Error. You can modify the symbology of the Facilities layer in the Layer Properties dialog box.
When a new service area analysis layer is created, the Facilities class is empty. It is populated only when network locations are added into it. At least one facility is necessary to create a service area.
Facility properties
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Input field |
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ObjectID |
The system-managed ID field. |
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Shape |
The geometry field indicating the geographic location of the network analysis object. |
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Name |
The name of the network analysis object. |
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Attr_[Impedance] (for instance, Attr_Minutes, where Minutes is the impedance for the network) |
This property stores the value of impedance for the facility. Adding a value to this property reduces the reach of the service area. For example, if you are finding the service area for three facilities using drive time as impedance, the property Attr_DriveTime can be used to store the amount of time spent at the facility. For example, when calculating service areas that represent fire station response times, Attr_DriveTime can store the turnout time, which is the time it takes a crew to don the appropriate protective equipment and exit the fire station, for each fire station. Assume Fire Station 1 has a turnout time of two minutes and Fire Station 2 has a turnout time of three minutes. If a 5-minute service area is calculated for both fire stations, the actual service area for Fire Station 1 would be three minutes (since 2 of the 5 minutes would be required as turnout time). Similarly, Fire Station 2 would have an actual service area of only two minutes.
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Breaks_[Impedance] (for instance, Breaks_DriveTime, where DriveTime is the impedance for the network) |
You can store different polygon break values for each service area facility in the Breaks_[Impedance] property. This means, if you have two facilities, you can generate 5-minute, 10-minute, and 15-minute service area polygons for one facility, and 3-minute, 6-minute, 9-minute, 12-minute, and 15-minute service area polygons for the second facility.
The value specified in the Breaks_[Impedance] property overrides the Default Breaks analysis layer setting. If no value for the Breaks_[Impedance] property is specified, service area polygons are generated for the facility based on the Default Breaks setting. |
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Network location fields
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Together, these four properties describe the point on the network where the object is located. |
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CurbApproach |
The CurbApproach property specifies the direction a vehicle may arrive at and depart from the facility. If the curb approach is confined to one side of the vehicle, it could further limit the reach of the service area. There are four options for the CurbApproach value:
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Input/Output field |
Description |
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Status |
This field is constrained by a domain of values, which are listed below (their coded values are shown in parentheses).
After a solve operation, the status can be modified using one of the following status values:
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Polygons class
The polygons network analysis class stores the resultant service area polygons. As with other feature layers, its symbology can be accessed from the Layer Properties dialog box of the feature layer.
When a new service area analysis layer is created, the Polygons class is empty. It is populated only when the analysis layer is solved. Once the service area is computed, the polygons are stored in the feature layer and are listed on the Network Analyst window.
Polygon properties
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Output field |
Description |
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ObjectID |
The system-managed ID field. |
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Shape |
The geometry of the polygon, which is stored internally. |
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Name |
The name of the service area polygon is based on the name of the associated facility and the break range; for instance, Graphic Pick 1: 0.0 – 5.0 would represent a polygon that covers all traversable edges within five minutes from the facility, Graphic Pick 1. |
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FacilityID |
The unique ID of the associated facility. |
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FromBreak |
The lower bound of the polygon's break range. |
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ToBreak |
The upper bound of the polygon's break range. |
Lines class
The Lines class stores the resultant service areas as linear features and represents the network edges that can be reached within the given impedance. Lines are a truer representation of a service area since the service area is based on measurements along the network.
Service area lines are not generated by default during a service area analysis; you can choose to generate them. Check Generate Lines on the Line Generation tab of the service area analysis layer's Layer Properties dialog box.
The service area lines feature layer can be symbolized in the same manner as other line feature layers.
Line properties
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Output field |
Description |
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ObjectID |
The system-managed ID field. |
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Shape |
The geometry of the line, which is stored internally. |
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FacilityID |
The unique ID of the associated facility. |
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FromCumul_[Impedance] (for instance, FromCumul_Miles or FromCumul_Minutes) |
This field contains the cumulative cost of the path from the facility to the beginning of this line feature. The impedance of the adjacent junction at the beginning of the line is included in this value. This field is generated for the impedance attribute and any accumulation attributes. |
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ToCumul_[Impedance] (for instance, ToCumul_Miles or ToCumul_Minutes) |
This field contains the cumulative cost of the path from the facility to the end of this line feature. The impedance of the adjacent junction at the end of the line is excluded from this value. This field is generated for the impedance attribute and any accumulation attributes. |
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SourceID |
Each service area line traverses a feature from a network source feature class. This field specifies the unique ID of the source feature class the traversed feature is a part of. The SourceID field is only present if Include Network Source Fields is checked before solving. The Include Network Source Fields check box is on the Line Generation tab of the Layer Properties dialog box. |
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SourceOID |
The ObjectID of the underlying source feature that is traversed by the service area. The SourceOID field is only present if Include Network Source Fields is checked before solving. The Include Network Source Fields check box is on the Line Generation tab of the Layer Properties dialog box. |
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FromPosition |
Specifies where along the underlying source feature the service area line begins.
The FromPosition field is only present if Include Network Source Fields is checked before solving. This check box is on the Line Generation tab of the service area analysis layer's Layer Properties dialog box. |
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ToPosition |
Specifies where along the underlying source feature the service area line ends.
The ToPosition field is only present if Include Network Source Fields is checked before solving. This check box is on the Line Generation tab of the service area analysis layer's Layer Properties dialog box. |
Point, line, and polygon barriers
Barriers serve to temporarily restrict, add impedance to, and scale impedance on parts of the network. When a new network analysis layer is created, the barrier classes are empty. They are populated only when you add objects into them—but adding barriers is not required.
Barriers are available in all network analysis layers; therefore, they are described in a separate topic.
Service area analysis parameters
Analysis parameters are set on the Layer Properties dialog box for the analysis layer. The dialog box can be accessed different ways:
Learn about opening the network analysis Layer Properties dialog box
The Analysis Settings tab
The following subsections list parameters that you can set on the analysis layer. They are found on the Analysis Settings tab of the analysis layer's Layer Properties dialog box.
Impedance
Any cost attribute can be chosen as the impedance, which is accumulated while determining the service area. For instance, choosing a Minutes attribute results in service areas based on time.
Restrictions
You can choose which restriction attributes should be respected while solving the analysis. Restrictions, such as Oneway, should be used when finding solutions for vehicles that must obey one-way streets (for instance, nonemergency vehicles). If your network dataset contains additional restriction attributes, such as weight limit or height limit, those could be used as well.
Restriction attributes can also be used in conjunction with dynamic attributes. For example, an edge could be restricted if the vehicle is taller than the height of a tunnel.
Default Breaks
The extent of the service area to be calculated is specified with the Default Breaks text box. For instance, a default break of 10 creates service areas of 10 units (for instance, minutes or miles) from the facilities. The unit is determined by the cost attribute chosen for the Impedance property.
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The Default Breaks property is used when a facility's Breaks_[Impedance] value is null. Suppose you have two facilities, A and B, for which you want to find service areas using DriveTime as the impedance. Facility A has a Breaks_[Impedance] (in this case, Breaks_DriveTime) value of 3. Facility B has no value for its Breaks_DriveTime property. When you find the service area with a default polygon break of 5 minutes, Facility B will have a 5-minute service area, whereas facility A will have a 3-minute service area.
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Note:The default polygon breaks parameter assigns breaks to facilities that do not have individual break values assigned (stored in the Break_[Impedance] property).
Multiple polygon breaks can be set to create concentric service areas. For instance, if you wanted to find 2-, 3-, and 5-minute service areas for the same facility, you would enter 2 3 5 in the Default Polygon Breaks text box (the numbers 2, 3, and 5 should be separated by a space).
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Direction
You can choose to create a service area by accumulating impedance in the direction away from or toward the facility. On a network with one-way restrictions and different impedances based on direction of travel, this would result in different service areas. The direction you should choose depends on the nature of your service area analysis. The service area for a pizza delivery store, for example, should be created away from the facility since pizzas are delivered from the store to the customer. Alternatively, a hospital should choose the opposite direction since the urgent part of the trip for an incoming patient is going to the hospital, not returning home afterwards.
U-turns at Junctions
ArcGIS Network Analyst can allow U-turns everywhere, nowhere, only at dead ends (or culs-de-sac), or only at intersections and dead ends. Allowing U-turns implies the vehicle can turn around at a junction and double back on the same street.
Ignore Invalid Locations
This property allows you to ignore invalid network locations and solve the analysis layer from valid network locations only. If this option is not checked and you have unlocated network locations, the solve may fail. In either case, the invalid locations are ignored in the analysis.
The Polygon Generation tab
Generate Polygons
This option is checked by default. Unchecking it allows you to calculate service areas without generating polygons. (You can check the Generate Lines check box on the Line Generation tab to create service area lines instead of, or in addition to, polygons.)
Polygon Type
You can choose to create quick, generalized polygons or detailed polygons.
- Generalized—Generalized polygons are generated quickly and are fairly accurate, except in the fringes. The generalizing of polygons may result in islands of unreached elements being covered.
- Detailed—Detailed polygons model the service areas more accurately and thus may result in islands of unreached areas. Expect detailed polygons to take noticeably longer to generate than generalized polygons.
- Trim Polygons—The polygons containing the network edges at the periphery of the service area can be further trimmed to be within the specified distance of these outer network edges. By default, this value is 100 meters.
If your data is of an urban area with a gridlike network, the difference between generalized and detailed polygons would be minimal. However, for mountain and rural roads, the detailed polygons may present significantly more accurate results than generalized polygons.
Multiple Facilities option
There are three options available for generating polygons for multiple facilities:
- Overlapping—This option creates individual polygons for each facility. The polygons can overlap each other.
- Not overlapping—This option creates individual polygons that are closest for each facility. The polygons do not overlap each other.
- Merge by break value—This option joins the polygons of multiple facilities that have the same break value.
Overlap Type
You can choose to create concentric service area polygons as disks or rings.
- Rings do not include the area of the smaller breaks. This creates polygons going between consecutive breaks.
- Disks are polygons going from a facility to a break. If you create 5- and 10-minute service areas, then the 10-minute service area polygon will include the area under the 5-minute service area polygon as well as the area from the 5-minute to the 10-minute break.
Exclude Sources
The option to exclude source feature classes from service area generation is available for service area analyses on multimodal networks. The geometries of features in excluded edge network sources are omitted from all service area polygons.
For example, while creating a drive time service area in a multimodal network, you should choose to exclude the rail lines from polygon generation so as to correctly model where a vehicle could travel (because an automobile cannot travel on rail lines). If the rail sources are not excluded, then rail lines that are not traversed could create unreached areas in the service area polygon.
Excluding a network source from service area polygons does not prevent those sources from being traversed. Excluding sources from service area polygons only influences the polygon shape of the service areas. If you want to prevent traversal of a given network source, you must create an appropriate restriction when defining your network dataset.
The Line Generation tab
Generate Lines
The Generate Lines check box provides the ability to create service area lines based on the features that fall within the specified impedance. This box is unchecked by default.
Generate Measures
Check this check box to create measures for your service area lines. This adds linear referencing information to the output lines to aid in the usage of service area lines for functions such as dynamic segmentation for events.
Split Lines At Breaks
Check this check box to split every line that intersects a break into two lines.
Include Network Source Fields
Adds the SourceID, SourceOID, FromPosition, and ToPosition values of the input feature that is traversed by the service area edges. This makes it easy to join the results of the service area lines to the original source data.
Overlap Options
You can choose to have your lines overlap or not overlap.
If you choose Overlapping, and if two facilities have service area lines that are coincident, there are two features there, one for each facility's service area line. If you choose Not Overlapping, then there is only one service area line, and it is associated with the closest (least impedance) facility.
The Accumulation tab
Under the Accumulations tab, you can choose cost attributes from the network dataset to be accumulated on the service area line objects. These accumulation attributes are purely for reference; the solver only uses the cost attribute specified by the analysis layer's Impedance parameter to calculate the service area.
For each cost attribute that is accumulated, two fields are added to the output lines: FromCumul_[Impedance] and ToCumul_[Impedance].
The Network Locations tab
The parameters on the Network Locations tab are used to find network locations and set values for their properties.